Field of the Invention
The present invention relates to an optical scanning type object detection device capable of detecting an object or the like which invades a detection area.
Description of the Related Art
In recent years, as crime prevention awareness rises, there is an increasing demand for a monitoring system capable of accurately detecting an object that has entered the detection area. As a method of detecting such an object, a radio wave radar which transmits radio waves to detect reflected waves has been proposed. However, it is difficult to accurately identify a position of a distant object from the viewpoint of resolution.
In contrast, WO 2011/021103 A discloses a TOF (time of flight) type measurement technique of emitting a laser beam while scanning with the laser beam, receiving a reflected beam reflected from a measurement object point, and acquiring distance information to the measurement object point on the basis of a time difference between an emitting time point and a receiving time point. The scanning with such a laser beam can be performed by reflecting a beam flux emitted from a laser light source by using a rotating mirror. An object detection device employing the TOF method has already been developed. However, in the object detection device employing the TOF method, in order to detect a weak reflected beam generated at the time of irradiating an object in a distance with a laser beam, generally, a light receiving element having a high amplification ratio such as an avalanche photodiode (APD) is used. In addition, in order to increase resolution of the object to be detected, in some cases, a plurality of light receiving elements which receive the reflected beam are arranged to ensure high resolution.
JP 2015-180956 A discloses a radar device including a rotating mirror unit including first and second mirror planes which are slanted with respect to a rotation axis and a projection system including at least one light source emitting a beam flux toward an object through the mirror unit, wherein the beam flux emitted from the light source is reflected on the first mirror plane of the mirror unit, after that, is propagated toward the second mirror plane, is further reflected on the second mirror plane, and is scan-projected on the object according to rotation of the mirror unit. In the case of using such a mirror unit, the beam flux emitted from the projection system is reflected on the rotating first and second mirror planes, after that, is irradiated toward the object, is reflected on the object, is reflected again on the first and second mirror planes, and after that, is incident on a light receiving system. Therefore, in principle, only the reflected beam of the projected beam is incident on the light receiving system, and thus, there is an advantage in that the device has resistance to disturbance light, has high resolution, and has a wider field of view.
In JP 2015-180956 A, it is disclosed that a plurality of light sources are used, and thus, the number of scan lines can be increased without deterioration in longitudinal distortion. However, with a configuration disclosed in JP 2015-180956 A, detection range around the rotation axis of the mirror unit is limited.
In contrast, the specification of U.S. Pat. No. 7,969,558 discloses an optical measurement device which rotates a unit where a plurality of light sources and light receiving elements are two-dimensionally arranged to be capable of receiving reflected beams from an object with respect to a laser beam emitted from a light source one by one by using light receiving elements. According to the optical measurement device, object detection can be performed over a range of 360°.
However, in the optical measurement device in the specification of U.S. Pat. No. 7,969,558, due to providing a plurality of light sources and light receiving elements, cost becomes very large, and how the light sources and light receiving elements can be power-supplied and controlled from the outside. For example, if a plurality of the light sources and the light receiving elements are attempted to be power-supplied or communication-controlled from the outside by using a contact type rotary connector or the like, the configuration becomes large, and also noise generation or treatment difficulty occurs. In contrast, in recent years, non-contact type connectors capable of performing wireless power supply by using electromagnetic induction by coils or performing wireless communication by using infrared rays, light, or the like have also been developed. Although it may be considered that these connectors are applied to the technique disclosed in the specification of U.S. Pat. No. 7,969,558, cost may increase, or the configuration may be complicated.